Variable free stream buffer

ABSTRACT

A buffer device for maintaining a high level of infrared output from an airborne target/source composed of a plurality of hollow tubes arranged together in a bundle and attached in circumferential relation around the base of the source. By progressively decreasing the length of the tubes in a radially outward and predetermined manner, the free stream flow past the source may be progressively decelerated, on passing through the tubes, inwardly towards the source until the velocity thereof at the interface between the plume formed by hot gases emitting from the source, and the free stream flow is approximately matched, thereby minimizing turbulent mixing of and thus stabilizing the plume.

United States Patent [191 Iwanciow 1 Oct. 14, 1975 VARIABLE FREE STREAM BUFFER Bernard L. Iwanciow, Sunnyvale, Calif.

[22] Filed: Sept. 25, 1974 [21] Appl. No.: 509,202

[75] Inventor:

[52] U.S. Cl. 250/504; 250/503; 250/493; 239/265.25 [51] Int. Cl. G01J 1/00 [58] Field of Search 250/493, 503, 504, 505, 250/517; 60/317, 324; 239/265.25, 265.27

[56] References Cited UNITED STATES PATENTS 2,974,481 3/1961 Smith 239/265.25 3,135,291 6/1964 Kepler et a1. 239/265.27 3,419,709 12/1968 Bell 250/493 3,441,218 4/1969 Bucher 239/265.25

Primary Examiner-James W. Lawrence Assistant ExaminerB. C. Anderson Attorney, Agent, or Firm.loseph E. Rusz; Arthur R. Parker ABSTRACT A buffer device for maintaining a high level of infrared output from an airborne target/source composed of a plurality of hollow tubes arranged together in a bundle and attached in circumferential relation around the base of the source. By progressively decreasing the length of the tubes in a radially outward and predetermined manner, the free stream flow past the source may be progressively decelerated, on passing through the tubes, inwardly towards the source until the velocity thereof at the interface between the plume formed by hot gases emitting from the source, and the free stream flow is approximately matched, thereby minimizing turbulent mixing of and thus stabilizing the plume.

7 Claims, 2 Drawing Figures US. Patent Oct.14,1975 Sheet 1 of2 3,912,934

U.S. Patent Oct. 14, 1975 Sheet 2 of2 3,912,934

VARIABLE FREE STREAM BUFFER RIGHTS OF THE GOVERNMENT The invention described herein may be manufac tured and used by or for the Government of the United States for all governmental purposes without the pay ment of any royalty.

BACKGROUND OF THE INVENTION This invention relates generally to the field of infrared radiation and, in particular, to a novel means for maintaining the output from an airborne-type of infra red radiation source at a relatively high level.

In the development of infrared sources whose radiation is derived principally from a carbon-rich flame or plume, such as that from the flow of hot exhaust gases of a guided missile/rocket in flight, it has been observed that the degree of intensity and thus the level of output therefrom significantly degrades under operational conditions, which phenomenon naturally makes tracking and guidance of the missile extremely difficult, if not actually impossible, throughout the operating range thereof.

It is considered that the foregoing degradation of the airborne infrared radiation is the result of the much faster velocity of the free stream flow immediately surrounding the missile, as compared with that of the flame or plume of hot gases emitting from the missile and, of course, constituting the infrared source. This considerable difference in velocity establishes a turbulent recirculation at the base region of the plume and a rapid mixing between the free stream flow and plume which is manifested by a large drop in the infrared output of the source, as distinguished from that measured under test conditions where there is no free stream flow past the plume. It is, therefore, the object of the present invention to eliminate or at least substantially alleviate the aforementioned problem of turbulent recirculation between the free stream flow past an airborne infrared radiation source such as the aforesaid guided missile/- rocket and the plume of hot gases being generated thereby by combining a novel and yet simplified buffer device with the infrared source and thereby absorb the excess velocity of the free stream flow in a unique manner to be described hereinafter in the following summary and detailed description.

SUMMARY OF THE INVENTION The present invention consists in a new and improved combination of an infrared radiation source comprised of a plume of hot gases emanating from the base of a cone-shaped cavity which, however, could, in one example thereof, be represented by the exhaust nozzle of a guided missile/rocket, and a novel buffer assembly disposed around the cone-shaped cavity-source of infrared radiation and specifically operative to absorb the excess velocity between the free stream flow and that of the plume of hot gases to thereby prevent, minimize or, at least, delay any mixing between the said free stream and plume, which mixing results in dilution of plume and hence the degradation of the infrared output therefrom, as noted hereinbefore. In a basic form thereof, the aforesaid buffer assembly of the instant invention constitutes a structure fixed in stationary position and circumferential relation to and around the cone-shaped cavity and comprised of a bundle of hollow tubes constructed of varying and progressively decreasing lengths in a radially outward direction away from the outer wall of the cone-shaped cavity and the plume emanating therefrom, with, therefore, the hollow tubes of the greatest length being the nearest to the plume.

The crux of the above-described arrangement of varying length-hollow tubes, which collectively act as a free stream buffer device, is that, as the free stream immediately around the guide missile/rocket in flight, attempts to flow past the said rocket and, of course, the cone-shaped cavity and infrared radiation producing plume of hot gases emanating therefrom, it enters the bundle of hollow tubes forming the key feature of the present invention, where a substantial portion of its velocity is absorbed by the said flow being progressively decelerated in direct proportion to the length of the particular set of tubes, Naturally, the longer the tube, the greater the deceleration. The net effect is that, with the progressively increasing lengths of the said tubes inwardly towards the plume, a free stream velocity gradient is developed from the outer edge of the bundle of tubes to the boundary of the plume. In this regard, it is noted that, as is specifically taught by the improvement of the instant invention, by properly selecting the various lengths and, therefore, the overall contour of each of the inventive buffer tubes to be used for a particular application and vehicle velocity, the velocity at the interface between the plume and free stream may be substantially matched, thus substantially eliminating the previously-described dilution of the plume and resulting loss of intensity of the infrared output therefrom that would otherwise occur from the turbulent recirculation and rapid mixing of the free stream flow and plume in other airborne infrared sources not equipped with the preesent buffer device. Therefore, with such elimination of any significant plume dilution, the infrared radiation is thereby maintained at a relatively high and constant level, thereby more readily enabling its detection, tracking and the guidance of the guided missile/rocket so equipped throughout its entire operating range.

It is emphasized that the foregoing use of a fixed or stationary bundle of hollow tubes surrounding the base region of the infrared source is suitable for a selected guided missile/rocket air speed and fixed velocity of flow of the plume of gases emitting therefrom, since the previously-referred to free stream velocity gradient can be determined for particular flow conditions by predetermining the size and the respective lengths and therefore contours of the free stream-buffer tubes to be used for a particular application. However, the basic form of the invention of FIG. 1 may be further improved, as disclosed specifically in FIG. 2, by enabling the geometry of the inventive free stream-buffer device to be changed in a unique manner and simply by adding to, or imbedding in each of the previously described fixed or stationary free stream-buffer tubes a slidable or telescopic tube, so that the overall length and therefore contour of each of the inventive tubes may be varied by adjusting the extended or telescopic position of each of said slidable tubes relative to and within the stationary tube corresponding thereto and, in this unique manner, automatically adjust the velocity gradient to one that effects a match or substantial match between the velocities of the free stream and plume flow, and thus specifically accommodate different and new sets of flow conditions by equalizing the particular free stream flow velocity to that of the said plume.

Other objects and advantages of the invention will readily appear hereinafter in connection with the following disclosure, taken with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partly broken-away and schematic, longitudinal sectional view of the basic combined infrared radiation source and free stream buffer tube of the present invention in which a system of fixed hollow tubes are used; and

FIG. 2 is a second longitudinal sectional view, partly broken-away and schematic, and similar to FIG. 1, but illustrating a modified form of the invention in which an additional, telescopic tube is used in each of the free stream buffer-fixed tubes to facilitate use of the inventive system for different flow conditions.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring specifically to FIG. 1, the basic form of the new and improved combined infrared radiation source and free stream-buffer assembly of the present invention is indicated generally at as including, in part, an infrared radiation device 11 that includes a coneshaped cavity section, at 14, from which may emanate an exhaust flame or plume of hot gases that actually constitute the source of infrared radiation, the base region of which being located in the general area donated by the reference numeral 12. The said infrared radiation device 11 could, of course, be representative of a guided missile/rocket in flight, if desired, with the free stream flow being indicated by the arrow A, and the description is made hereinafter with specific reference to the device 11 only for the sake of clarity with the understanding that the invention is readily applied to an airborne device, such as the aforementioned guided missile/rocket without departing from the true spirit or scope thereof.

In general, the infrared source may consist of a flame or plume of hot gases emanating from the base region of a cone-shaped cavity 14 (FIG. 1), which base region has been indicated at the previously noted reference numeral 12. The mass flow rate of this plume is generally quite low, having been found to be for the type of infrared radiation device configuration shown generally at 11 to be on the order of from 0.01 to 0.1 pounds per second. In this connection, for a typical infrared radiation source burner used for test purposes, for example, and having a nominal exit area of between 10 to 50 square inches and assuming a gas flow from the end of the burner to be in a cylindrical column, the typical velocity of flow of the plume resulting from the burner operation falls in the range of from between 4 to ft per second for the aforementioned 0.01 pounds per second rate and 40 to 200 ft per second for the 0.1 pounds per second rate. On the other hand, the free stream velocity, as represented at A, typically falls between 200 to 1000 ft per second. The problem then is clearly to slow free stream velocity to match or at least approach the velocity of the plume at the base region 12 and thus eliminate or substantially eliminate the previously-mentioned turbulent recirculation being normally established at the plume base region 12 by the free stream flow.

For a selected air speed and plume flow rate, the unique means of decreasing the velocity of the free stream flow A is to place in a unqiue combination with the aforementioned infrared radiation device 11, or, in other words, with a guided missile/rocket represented thereby, the novel free stream-buffer assembly, indicated generally at 13 (FIG. 1) and taught by, and constituting the key feature of the present invention. Said buffer assembly 13, in the basic inventive form of FIG. 1, simply comprises a plurality of fixed or stationary tubes 13a arranged in a bundle and attached in circumferential relation to the periphery of the infrared radiation device 11 at and around the base region 12 of the plume thereof. As is clearly illustrated in the said FIG. 1, the said tubes 13, which are, of course, hollow in configuration, are placed in the free stream flow A immediately adjacent to, and for some radial distance outwardly of the periphery of the infrared radiation device 11. The hollow buffer tubes 13 are, again as taught by the present invention, uniquely made of progressively decreasing lengths with the longer tubes located nearest to the plume-base region 12, and the shortest tubes nearest the free stream A. Thus, as the free stream A passes through the said bundle of tubes 13, it is decelerated with the greatest amount of deceleration naturally occurring in the longer tubes. The overall net effect thereof is the unique development of a free stream velocity gradient from the outer edge of the free stream buffer to the boundary of the plume-base region 12. In accordance with the novel teachings of the present invention, with the above arrangement of buffer tubes in a bundle and decreasing in length in a radially outward direction, by properly preselecting the length and contour of the buffer tubes 13, the velocity at the interface or, in other words, at the boundary between the plumebase region 12 and the free stream A may be essentially matched, thereby substantially preventing the previously described turbulence and thus minimizing the turbulent mixing and consequently effecting stabilization of the plume and, of course, thereby maintaining the infrared output therefrom at the desired relatively high and constant level.

With particular reference to FIG. 2, a modified form of the combined infrared radiation source and free stream-buffer assembly is indicated generally at 15 as again including an infrared radiation device, at 16, incorporating a cone-shaped cavity 17 from which may emanate a flame or plume, the base of which being disposed at the area indicated generally at 18, and a free stream buffer device-hollow tube assembly, indicated generally at 19. The latter consists uniquely of a first plurality of fixed or stationary hollow tubes, as at 20 and 21, which are similar to the tubes 13 of FIG. 1 and are fixedly attached to the periphery of the device 16 at or adjacent the base region 18 of the plume, and, in accordance with the improvement of this modification, a second plurality of movable free stream-buffer tubes, as at 22 and 23, which are made slidably mounted or positionable within said fixed or stationary tubes, as at 20 and 21 by any of a number of well-known and already available slidable mounting means (not shown). With this modified system, as either the free stream velocity or the velocity of the plume is changed, the length of the buffer tubes may be changed along with their overall contour simply by slidably or telescopically positioning the movable tubes, as at 22, 23, at different levels within their respective fixed tubes, 20, 21,

to thereby produce a new free stream velocity gradient compatible with the new set of flow conditions to thereby match or approximately match the free stream flow and plume flow velocities.

Thus, a new and novel means has been developed by the present invention of stabilizing the flame or plume of gases resulting from the emission thereof from selected infrared radiation sources, such as a guided missile/rocket in flight, whereby the normal turbulent mixing between the free stream flow and the plume, because of the significant difference in their velocities, is substantially eliminated by an arrangement of variable length, stationary free stream-buffer tubes disposed around the circumference of the plume-base region and progressively decreasing the flow velocity of the free stream inwardly towards the plume until the velocities thereof substantially match. In a second embodiment, the aforementioned stationary tubes each incorporate a slidable tube telescopically positionable in a corresponding fixed tube and adjustably positioned therewithin. By adjusting each of the said slidable tubes in a preselected extended position within the fixed tube corresponding thereto, the inventive series of variable length buffer tubes may be respectively and collectively adjusted to thereby ensure the matching of a large range of free stream flow and plume velocities to thus avoid any significant recirculation between, and, therefore, mixing of the free flow stream and plume.

Although the foregoing description is made with specific reference to the combination of a unique system of hollow tubes as the free stream-buffer, with an infrared radiation device, such as a guided missile/rocket in flight, it is to be understood that other types of free stream-buffer devices may also be used without departing from the true spirit or scope of the invention, such as, for example, a truncated cone-shaped, hollow disc element mounted on, and around the periphery of the infrared device 11 and which would incorporate a series of air passages of the varying lengths, as taught by the improvement of the present invention, to thereby provide the requisite progressive deceleration of the free stream flow and establishment of the previously described free stream velocity gradient.

I claim:

1. A combined infrared radiation source and free stream-buffer assembly, comprising; an airborne infrared radiation device emitting a plume of relatively low speed, hot gases constituting the specific infrared radiation source and surrounded by a relatively high speed, free stream flow; and free stream-buffer means attached to the outer periphery of said airborne device at the area thereof adjacent the base region of the plume of hot gases and extending radially outwardly into the path of the free stream flow, and incorporating built-in, open-ended and parallel-extending air passage means oriented in an upstream direction facing, partially entrapping and decelerating the relatively high speed, free stream flow to approximately the relatively slow speed flow of the plume of gases at the boundary therebetween to thereby substantially prevent the instability effect on the plume from the normal turbulent mixing of the free stream flow therewith, and therefore prevent a substantial reduction in the infrared intensity.

2. In a combined infrared radiation source and free stream-buffer assembly as in claim 1, wherein the builtin air passages of said free stream-buffer means progressively increase in length inwardly towards said infrared radiation device in a degree relative to each other and by increments predetermined for a selected air-speed and plume flow rate to thereby produce a free stream-velocity at the interface between the plume and free stream.

3. in a combined infrared radiation source and free stream-buffer assembly as in claim 2, wherein said free stream-buffer means comprises a bundle of variable length, hollow tubes respectively incorporating said built-in air passages of progressively increasing length in a radially inward direction.

4. In a combined infrared radiation source and free stream-buffer assembly as in claim 2, wherein said free stream-buffer means comprises a truncated coneshaped, hollow disc element incorporating said built-in air passages therethrough.

S. In a combined infrared radiation source and free stream-buffer assembly as in claim 1, wherein said free stream-buffer means comprises a bundle of variable length, hollow tubes incorporating said air passages and fixed in position on the periphery of said infrared radiation device.

6. In a combined infrared radiation source and free stream-buffer assembly as in claim 1, wherein said free stream-buffer means comprises a bundle of telescopi cally adjustable, hollow tubes incorporating said air passages.

7. in a combined infrared radiation source and free stream-buffer assembly as in claim 1, wherein said free stream-buffer means comprises; a first set of hollow tubes disposed around the outer circumference of said infrared device and being of progressively increasing lengths in a radially inward direction; and a second set of hollow tubes each telescopically received and adjustable in said first-named tubes a measured extent compatible with and predetermined for that required to match the velocities of the free stream and the rate of flow of the plume at the boundary therebetween.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORREQHON PATENT NO. 3 912,934

DATED October 14, 1975 INVENTOR(S) Bernard L. Iwanciow It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 36, change "preesent" to present Column 6, line 18, for claim 2, after "velocity" insert gradient compatible with the approximate matching of the velocity fiigncd and Sealed this twentieth Day of Aprill976 [SEAL] A ttest:

RUTH C. M A SON C. MARSHALL DANN Arresting Officer mnmr'ssimicr of Parents and Trademarks 

1. A combined infrared radiation source and free stream-buffer assembly, comprising; an airborne infrared radiation device emitting a plume of relatively low speed, hot gases constituting the specific infrared radiation source and surrounded by a relatively high speed, free stream flow; and free stream-buffer means attached to the outer periphery of said airborne device at the area thereof adjacent the base region of the plume of hot gases and extending radially outwardly into the path of the free stream flow, and incorporating built-in, open-ended and parallelextending air passage means oriented in an upstream direction facing, partially entrapping and decelerating the relatively high speed, free stream flow to approximately the relatively slow speed flow of the plume of gases at the boundary therebetween to thereby substantially prevent the instability effect on the plume from the normal turbulent mixing of the free stream flow therewith, and therefore prevent a substantial reduction in the infrared intensity.
 2. In a combined infrared radiation source and free stream-buffer assembly as in claim 1, wherein the built-in air passages of said free stream-buffer means progressively increase in length inwardly towards said infrared radiation device in a degree relative to each other and by increments predetermined for a selected air-speed and plume flow rate to thereby produce a free stream-velocity at the interface between the plume and free stream.
 3. In a combined infrared radiation source and free stream-buffer assembly as in claim 2, wherein said free stream-buffer means comprises a bundle of variable length, hollow tubes respectively incorporating said built-in air passages of progressively increasing length in a radially inward direction.
 4. In a combined infrared radiation source and free stream-buffer assembly as in claim 2, wherein said free stream-buffer means comprises a truncated cone-shaped, hollow disc element incorporating said built-in air passages therethrough.
 5. In a combined infrared radiation source and free stream-buffer assembly as in claim 1, wherein said free stream-buffer means comprises a bundle of variable length, hollow tubes incorporating said air passages and fixed in position on the periphery of said infrared radiation device.
 6. In a combined infrared radiation source and free stream-buffer assembly as in claim 1, wherein said free stream-buffer means comprises a bundle of telescopically adjustable, hollow tubes incorporating said air passages.
 7. In a combined infrared radiation source and free stream-buffer assembly as in claim 1, wherein said free sTream-buffer means comprises; a first set of hollow tubes disposed around the outer circumference of said infrared device and being of progressively increasing lengths in a radially inward direction; and a second set of hollow tubes each telescopically received and adjustable in said first-named tubes a measured extent compatible with and predetermined for that required to match the velocities of the free stream and the rate of flow of the plume at the boundary therebetween. 